The use of inflatable structures is of interest for applications in which it is desired to provide storage facilities, habitats, laboratories, or the like in remote or isolated locations. Such an inflatable structure may be conveniently transported to a desired location or region in a reduced-volume, non-inflated mode and deployed at the site by inflating the structure, thereby increasing its volume and quickly forming a self-supporting structure. Thus, when it is desired to deploy such a structure in a remote location, or in a region subject to severe environmental conditions, for example, it is advantageous to be able to transport the structure to the desired location in a reduced-volume, non-inflated mode, and to enable its convenient deployment at the remote site. Thus, the time and difficulty entailed in its deployment at the site may be substantially reduced, thereby avoiding prolonged exposure of workers to hazardous conditions during the deployment process.
The use of such an inflatable structure or module is also a means for providing a deployed structure of substantial size and interior volume, substantially greater than that of a conventional, rigid structure of the same mass. As noted, such inflatable structures have been proposed for use as laboratories, human habitats or storage facilities in remote or isolated areas. For example, they are considered advantageous for use as vehicles or modules intended for applications in exoatmospheric space, e.g., vehicles intended for use during orbital or extra-orbital missions, including those intended as habitats on the moon or planets. For such applications, the inflatable structures are launched and placed in orbital or other desired trajectories while in a collapsed, non-inflated mode and then inflated, thereby providing a space module having substantially larger volume than conventional modules of equivalent mass and initial size.
Conventional, non-inflatable or hard-shelled space modules, such as those forming sections of the International Space Station (ISS), have been delivered to the ISS within the cargo bay of the National Aeronautics and Space Administration (NASA) Space Shuttle. In order to minimize the difficulty of tasks required during assembly and deployment of the modules in space, such modules are fabricated and assembled before being loaded into the cargo bay of the Space Shuttle, or other suitable launch vehicle, thereby reducing the complexity of operations required of the astronauts during final assembly and adjustments of the module in space.
Because such conventional space modules have been carried within the cargo bay of the Space Shuttle, their external dimensions must be compatible with the interior dimensions of the cargo bay of the Space Shuttle. Accordingly, their size and configuration have been limited by the internal dimensions and configuration of the Space Shuttle cargo bay. Although sufficient for some applications, larger modules are desirable for other applications, for which the use of inflatable modules is advantageous.
Further advantages of such inflatable modules for space applications include the fact that they are substantially lighter than conventional, “hard shell” modules of equivalent deployed size, due to the fact that such an inflatable module does not require a reinforced, outer metallic skin and associated support structures. A further advantage is the fact that although the diameter of the inflatable module, before deployment, is small, relative to that desired in the deployed vehicle, after deployment the diameter may be substantially larger than that of the outer diameter of the cargo section of the Space Shuttle, or other launch vehicles that may be used, thereby providing a deployed module having a large internal volume suitable for applications such as orbital laboratories, habitats, storage modules, etc. Publications relating to the design of such inflatable space modules include U.S. Pat. Nos. 6,974,109 and 6,938,858; United States Patent Application Publication No. US 2005/0108950 A1, published May 26, 2005, and U.S. Pat. Nos. 6,231,010 and 6,547,189. The construction of such space modules is disclosed in detail in U.S. Pat. Nos. 6,231,010 and 6,547,189, both of which are hereby incorporated by reference.
Whereas such inflatable structures have utility in a variety of applications and environments, their construction entails design considerations not typically experienced in the construction of conventional buildings, storage structures, rigid space modules, and the like. This is particularly the case with respect to space applications, wherein safety considerations are paramount, and wherein human lives are dependent upon the structural integrity and reliability of such structures. For example, such design considerations include factors relating to the integration of rigid panels, bulkheads, hatches, window frame assemblies, and the like into the flexible outer walls of such modules. As disclosed in the U.S. Pat. Nos. 6,231,010 and 6,547,189 patents, the flexible outer walls of such inflatable space structures are complex structures incorporating multiple layers formed of materials selected to perform respective functions. For example, and starting with the innermost layer and progressing outwardly, such flexible outer wall structures may include: an inner protective liner; at least one bladder of a gas-impermeable material; a structural restraint layer; a meteoroid orbital debris (M/MOD) shield assembly, and an outer protective layer. Structural loads resulting from the inflation of the inflatable module are born by the restraint layer, which may be a webbing comprising multiple, orthogonal strips of high tensile strength material such as Kevlar® or Vectran®.
As disclosed in the '010 and '189 patents previously incorporated by reference, inflatable structures or modules adapted for use in exoatmospheric space, in some applications, have been of elongated, cylindrical configuration. In such embodiments, they may include a longitudinally extending, rigid central core or truss assembly around which the flexible shell or outer wall structure is formed. Upon being inflated by the introduction of gas under pressure during deployment, the module expands, and the flexible wall structure is thus stretched outwardly into an elongated, substantially cylindrical shape, the elongated central core extending longitudinally and coaxially along the length of the inflatable structure. As also disclosed in the referenced '010 and '189 patents, in one embodiment, end portions of the flexible wall structure are attached to respective end portions of the longitudinal core and, when deployed, form partially hemispherical end portions. As will be understood by those in the art, when inflated, the flexible wall structure is subject to tensional forces caused by the increased interior pressure, i.e., the differential pressure between that of the interior volume of the structure and the external environment, which in the case of a vehicle in space is a substantially perfect vacuum.
Tensional forces exerted on the flexible wall structure are largely sustained by the restraint layer, which in some embodiments comprises a webbing formed of interwoven straps. After deployment, pressures within an inflated module intended for use as a human habitat are typically in the range of approximately 8 to 15 pounds per square inch. Because such space modules, in their deployed, inflated mode, may be of substantial diameter, the tensional forces on the restraint layer may also be substantial, particularly forces exerted circumferentially of cylindrical portions of such modules. As will be understood by those in the art, the longitudinal forces, i.e., the forces exerted along the longitudinal axis of the module may be partially sustained by the rigid interior core and are generally less than the circumferential forces sustained by circumferentially extending straps.
Whereas the construction of such inflatable modules has been the subject of extensive development, complications exist with respect to certain design features. As previously stated, this is particularly the case with respect to the integration of rigid elements, such as bulkheads, panels, hatches, window assemblies, and the like, into the flexible wall structure. For example, if such a module is intended for use as a work area, laboratory, or habitat, it is often desirable to provide windows, doors, or the like in the module flexible wall structure. The provision of windows is of interest with respect to inflatable modules such as laboratories, human habitats, or the like intended for use in exoatmospheric space, particularly those that will be occupied for extended periods of time. In addition to the obvious human factors, the ability to view structures external of the module may be of importance during docking maneuvers, safety inspections, and the like.
However, the integration of mounting of a rigid structure in the flexible wall structure of such an inflatable module presents unique challenges to the designer. For example, if one or more window frame assemblies are to be integrated within such a flexible wall structure to permit visual observations through the windows, it is necessary, at each window, to form openings or “structural pass throughs” through the portions of the flexible wall structure in register with the window frame assembly. Thus, openings must be formed through the bladder, the inner and outer protective layers, and the flexible restraint layer, among others. To prevent the escape of gas under pressure from the interior of the module through such an opening, means must be provided for sealingly attaching the bladder to the periphery of the window frame. With respect to the restraint layer, each of the longitudinal and circumferential straps adjacent an opening, e.g., each of the orthogonally arrayed straps that intersect the window frame assembly must be terminated to form the opening in which the window frame assembly will be mounted. As will be discussed below, loops are preferably formed in the end portions of the straps adjacent the window frame assembly for facilitating their connection to the rigid window frame or panel, as described in the referenced '189 and '010 patents and as will be discussed further below.
For ensuring the physical integrity of the module, provisions must be made for securely attaching the looped end portions of the straps to portions of the window frame such that tension occurring as the module is inflated can be retained on all the straps, including those terminated at the windows, applying tensional loads on the straps as required both for maintaining a desired configuration and configuration of the module when inflated and for maintaining its structural integrity. Additionally, it is desirable to evenly distribute such loads and to prevent binding of the straps during movement and flexure of the flexible wall structure. As disclosed in the '189 and ‘610’patents, the end portions of the straps are advantageously looped around rollers rotatably supported by devises or the like mounted along the periphery of the window frames, whereby tensions on the upper and lower portions of the strap loops are substantially equalized, and whereby the straps may exert tension on the window frame from different directions without binding at their connection to the frame, and whereby tensional forces on the straps may be substantially equalized and consistently applied to the window frame.
The use of such structural pass-through panels, such as window frames, having rollers supported by devises adjacent the peripheral edges of the panel through which end portions of respective webbing straps are looped, and wherein circumferentially extending straps are interwoven with the longitudinal straps, is disclosed, for example, in the '189 patent. Also disclosed in the '189 patent are means for sealingly attaching the bladder of such an inflatable module to peripheral portions of rigid panels, window frames, or the like for preventing leakage of air from the interior of an inflated module around the frame and through the opening.
Further issues of concern with respect to the integration and interaction of the rigid and flexible components include the necessity of preventing damage to flexible layers, such as the bladder, restraint layer, and protective backing materials, as the module is unfolded and expanded during its inflation and deployment. Also, both during and after deployment, differential stresses and different reaction to stresses by rigid and flexible components are of concern and could result in undesirable degrees of strain on the flexible components if not properly compensated for and distributed. For example, and as will be understood by those in the art, tensional forces exerted on the flexible straps can result in a degree of elongation or stretching of the straps, whereas the same forces exerted on a rigid panel produce substantially no deformation of the panel. Thus, and as will be more fully understood from the disclosure to follow, means must be provided for reducing potentially deleterious, differential stresses on the respective flexible straps, for ensuring that such forces are evenly distributed, and for accommodating differing reactions to stress of the rigid and flexible components.
As will be understood from the description to follow, advantageous features of the present invention include the use of mechanisms for connecting circumferential and longitudinal webbing straps to one or more rigid panel members, such as window frames, such that tensional loads are equally distributed thereon and such that the loads on the straps are parallel to the major axes of the panel, so that bending moments on the panel and on elements mounted on the panel are reduced. As will be understood from the disclosure to follow, in preferred embodiments of the present invention, such non-axial forces are eliminated or substantially reduced.
Connecting mechanisms for connecting respective load bearing straps to such rigid panel structures, in some applications, have comprised attachment mechanisms affixed to the panels and mutually spaced along the edges of such panels, whereby the load-bearing straps supported by respective connecting mechanisms are maintained in mutually spaced, mutually parallel configuration. This spacing between adjacent straps has, in the past, been necessary because the connecting mechanisms, typically including clevis structures and rollers, are wider than the respective straps and are mutually spaced along the panel edge portions. As will be understood from the present disclosure, in mechanisms constructed in accordance with embodiments of the present invention, the mutually parallel straps connected to edge portions of such a rigid panel may be substantially contiguous to one another rather than being mutually spaced. This permits the use of a greater number of connecting means, and thus, a greater number of straps per unit of length along a given panel edge portion, thus distributing the loads through a greater numbers of straps than would be otherwise permitted and thereby reducing the loads sustained by the individual straps.
Another complication entailed in the integration of rigid structures into the flexible outer walls of such inflatable structures relates to the fact that, as previously noted, circumferentially directioned forces sustained by the cylindrical wall portion of a module after inflation are normally greater than those sustained in the longitudinal direction. As will be understood from the disclosure to follow, complications from such an effect are substantially alleviated in embodiments of the present invention. As previously suggested, a further complication relative to such inflatable structures which is addressed herein relates to the fact that, as pressure increases within the module during deployment, the flexible straps tend to stretch and elongate as they sustain their respective tensional loads. However, there is relatively little deformation or elongation of the rigid structures. Thus, elongation of the inflatable and rigid structures can differ, creating an uneven load distribution around the panel structure. If unaddressed, this fairly local effect could overload the inflatable shell and/or frame in that region.
With reference to the disclosure, although the embodiments illustrated in the accompanying drawings and described in detail herein relate primarily to applications of inflatable modules in exoatmospheric space, it should be understood that the invention is not limited to such applications and also has utility in various terrestrial and marine applications, particularly those in which it is desired to provide enclosed storage or habitat facilities at a remote location or under severe weather conditions, and in which it is desired to transport the facilities to such locations in a compact mode and to deploy them quickly and conveniently at the desired site.
Thus, the present invention provides structure for forming an improved interface between rigid and flexible components in an inflatable structure having a flexible outer shell or wall. In particular, the present invention resolves problems relating to the mounting of rigid panels, such as window frame structures, in the flexible walls of such inflatable structures and is adapted for reliable operation for extended periods in severe environments. The design and construction of the present invention and such inflatable structures, and the nature of the forces acting upon their various components, will be more fully understood and appreciated from the detailed disclosure to follow.